Dental glue, glue injector, and device for detecting injected glue

ABSTRACT

A paste formulation for dental use, a paste injector, and a system for detecting paste filling are disclosed. The paste formulation includes electric conductive material. The present invention also discloses the system for detecting paste filling comprising a paste injector containing electric conductive paste and an electric conductive member for electrically connecting the electric conductive paste to an external electrode, a current detector for detecting the current flowing through the electric conductive paste held in the container portion, and a current display device for indicating the current flowing through the electric conductive paste.

FIELD OF INVENTION

The present invention relates to a paste formulation, a tool, and asystem for root canal treatment, and more particularly relates to thepaste used for root canal filling, a paste injector, and a system usedtherewith.

BACKGROUND ART

In dental clinical treatments, root canal treatments are popularlyoperated. Among the root canal treatments, root canal filling isoperated at the final stage of the root canal treatment, and then theroot canal filling has large effects on prognosis of a damaged tooth.Since the length to an apical constriction varies from individualpatients, a length of the root canal must be measured. A method for thismeasurement includes, conventionally to measure an actual length of thetooth by using a reamer, a file, or a scale as detection probes for anx-ray photograph. Recently, a method for measurement of the root canallength using an impedance is widely used, because there is a case thatthe x-ray exposure is not adequate for a pregnant woman and theimpedance measurement is speedy and provides exact results.

The root canal length measurement by impedance conventionally uses aroot canal meter. A working length is then determined to be the reamerlength inserted in the root canal minus 1 mm which is indicated by apredetermined impedance previously measured depending on the conditionsof the instruments for measurement when a top of the reamer contacts theperiodontal membrane. Alternatively, the working length is determined asthe length that gives current or resistance being different by a certainvalue from the value which indicates contact to the periodontalmembrane.

A root canal filling material, or root canal filling agent such as afiller paste formulation conventionally used for the root canal fillingincludes a gutta percha point used together with various sealers, silverpoints and a filler in a paste formulation which may be formulated witha sustainable disinfectant or an accelerator for healing with osteoidscar.

Especially, a method for filling the paste formulation in the root canalportion includes filling the paste formulation through thereverse-rotated reamer operated by hand, filling by using a fillingdevice with a helical shape such as Rentulo plugger, or filling thepaste through a paste injector. However, the methods using the reamerand Rentulo plugger have disadvantages, because these methods require anextra procedure for measuring the root canal length and the specialdevice.

FIG. 9 shows a conventional method for filling the paste formulationinto the root canal by the injector. In the conventional root canalfilling method using the injector, the injector 1 shown in FIG. 9(a)filled with the paste formulation M is used. The injector 1 comprises acontainer portion 2 and an insert portion 3 which may be inserted intothe container portion 2. A tube for injection of the filler is disposedat a front end of the container portion 2 to form an injection portion4. In FIG. 9(a), the tip of the paste injection tube is inserted intothe root canal portion which has previously been spread widely.

In the conventional root canal filling method, as shown in FIG. 9(b),the paste formulation M is injected into the root canal while insertingthe filler injection tube into the root canal and pressing the insertportion 3 in the direction of the arrow A. When the filling iscompleted, the filler injection tube is drawn out from the root canaland then the root canal filling operation is completed.

When the root canal is filled by the injector, as described above, anadvantage to complete the injection easily and quickly may be providedwithout the procedure to measure the root canal length previously.However, this method has some disadvantages, that is, filling of thepaste to the apical constriction is unknown and the paste formulationmay irritate root peripheral tissues when the paste formulation isinjected beyond the apical constriction. When the filling is not enough,a dead space and/or residual pulps may be allowed to exist. Therefore,there are needs for the paste formulation, the paste injector, and thesystem for detecting the paste filling.

SUMMARY OF THE INVENTION

In the first aspect of the present invention, a paste formulation fordental use comprising electric conductive material may be provided.

In the first aspect of the present invention, the paste formulation isprovided, wherein the electric conductive material is powder.

In the first aspect of the present invention, the paste formulation fordental use may be provided, wherein the electric conductive material isselected from the group consisting of metal powder, metal oxide powder,coated inorganic powder by metal and/or doped metal oxide, carbonpowder, carbon whiskers, and whiskers integrated with metal.

In the first aspect of the present invention, the paste formulation fordental use may be provided, wherein the paste formulation includes atleast one compound selected from the group consisted of calciumhydroxide, hydroxy apatite, tricalcium phosphate.

In the first aspect of the present invention, the paste formulation fordental use may be provided, wherein the paste formulation includes atleast one compound selected from the group consisting of iodoform,barium sulfate, anhydrous zinc sulfate, aluminum sulfate, and zincoxide.

In the first aspect of the present invention, the paste formulation fordental use may be provided, wherein the paste formulation includes atleast one vehicle selected from the group consisting of silicone oil,guaiacol formaldehyde mixture, propylene glycol, dry ethanol, casteroil, liquid paraffin.

In the first aspect of the present invention, the paste formulation fordental use may be provided, wherein the paste formulation includes atleast one compound selected from the group consisting of iodoform,barium sulfate, anhydrous zinc sulfate, aluminum sulfate, and at leastone vehicle selected from the group consisting of silicone oil,guaiacol-formaldehyde mixture, propylene glycol, dry ethanol, casteroil, and fluid paraffin.

In the first aspect of the present invention, the paste formulation fordental use may be provided, wherein the paste formulation includes anx-ray contrast agent.

In the first aspect of the present invention, the paste formulation fordental use may be provided, wherein the electric conductive material ispresent between 5˜50 wt % based on a solid of the paste formulation.

In the first aspect of the present invention, the paste formulation fordental use may be provided, wherein the paste formulation includes atleast one compound selected from the group consisting of calciumhydroxide, hydroxy apatite, tricalcium phosphate not less than 30 wt %based on a solid of the paste.

In the second aspect of the present invention, a paste injector may beprovided. The paste injector comprises;

a container portion within which electric conductive paste is held,

an insert portion inserted into the container portion,

an injection portion for injecting the electric conductive pasteformulation into a constricted portion, and

an electric conductive member for electrically connecting theelectrically conductive paste formulation to an external electrode.

In the second aspect of the present invention, the paste injector may beprovided, wherein the electric conductive member comprises a terminalexposed at an end face of the insert portion inserted into the pastecontainer portion and contacting the electric conductive pasteformulation, a terminal disposed at the insert portion and exposedoutside the insert portion, and a lead line connecting between theterminals.

In the second aspect of the present invention, the paste injector may beprovided, wherein the electric conductive member is inserted through theinsert portion.

In the second aspect of the present invention, the paste injector may beprovided, wherein the electric conductive member comprises an endextending through an inner path of the injection portion, an end drawnout of the paste injector, and a lead line connecting between the ends.

In the third aspect of the present invention, a system for detectingpaste filling may be provided. The system comprises;

a paste injector comprising an electric conductive paste formulation andan electric conductive member for electrically connecting the electricconductive paste to an external electrode,

a current detector for detecting the current flowing through theelectric conductive paste formulation injected into a constrictedportion, and

a current display device for indicating the current flowing through theelectronic conductive paste.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows the paste injector according to the present invention;

FIG. 2 shows details of the paste injector according to the presentinvention;

FIG. 3 shows a second embodiment of the paste injector according to thepresent invention;

FIG. 4 shows an arrangement of a conventional system for impedancemeasurement used for detecting the working length;

FIG. 5 shows a method for the root canal length measurement using thereamer and the impedance;

FIG. 6 shows an arrangement for filing electric conductive paste D intothe root canal of the damaged tooth by the paste injector of a firstembodiment according to the present invention;

FIG. 7 shows an arrangement for filing electronic conductive paste Dinto the root canal of the damaged tooth by the paste injector of asecond embodiment according to the present invention in the samearrangement shown in FIG. 6;

FIG. 8 shows an electric circuit arrangement used for testing the pasteaccording to the present invention; and

FIG. 9 shows a conventional root canal filling method by a conventionalinjector.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention provides an electric conductive paste formulationfor dental treatment, i.e., an electric conductive paste formulation, apaste injector, and a system for detecting paste filling. Hereafter, theelectric conductive paste formulation, the paste injector, and thesystem for detecting paste filling will be described using the drawingsattached when necessary.

The electric conductive paste formulation according to the presentinvention may be formulated by mixing a suitable electric conductivematerial with conventional compositions for forming of calcium hydroxidepaste, zinc eugenol paste, iodoform paste, paraform-formaline paste.These conventional paste compositions may include Triozinc pasta whichis a mixture of paraform aldehyde, anhydrous zinc sulfate, aluminumsulfate, potassium sulfate, zinc oxide mixed with cresol, phenol, andcreosote; Kri 1 which is a mixture of iodoform powder, parachlorophenolcampher, menthol, lanolin, glycerin; Carbitar which is a mixture ofiodoform powder, calcium hydroxide powder, sulfathiazole powder,guanofuracin with a vehicle such as T-caine and guanofuracin; Bitapexwhich is a mixture of calcium hydroxide powder and iodoform powder withsilicone oil; FR which is a mixture of calcium hydroxide powder, zincoxide powder, barium sulfate powder, and a vehicle such asguaiacol-formaldehyde mixture, propylene glycol, dry ethanol, casteroil, liquid paraffin; Sealapex which comprises a polymer resin andcalcium hydroxide.

Other paste formulation such as Endofil which uses a polymeric materialas a base and the paste formulations which use hydroxy apatite ortricalcium phosphate may be useful, because such paste formulationsexhibit affinity to live tissues and accelerate hard tissues formation.These paste formulations may provide advantages that the formulation maybe absorbed by the tissues if the paste formulation runs out from theapical constriction. The above described calcium hydroxide, hydroxyapatite, tricalcium phosphate may be included in the electric conductivepaste in an amount not less than 30 wt %, more preferably not less than50 wt % based on the weight of solid contents in the electric conductivepaste formulation.

The electric conductive material suitably used in the present inventionmay include electric conductive powder so as to be mixed sufficientlywith the above described paste formulations. Such electric conductivepowder may have a particle size between 200 Å˜100 μm, more preferably,between 0.01˜80 μm, most preferably between 10˜50 μm in order to achievea good filing performance. Shapes of the electric conductive powder maybe a spherical shape, a needle shape, and a scale shape.

The powder may include metal powder such as, for example, gold powder,silver powder, copper powder, nickel powder, metal oxide powder such as,for example, ZnO, SnO₂, I₂O₃, ITO, various doped metal oxides such asantimony doped SnO₂, BaSO₄ coated with metal, SnO₂, or other electricconductive materials, TiO₂ powder coated by Ag, TiO₂ powder coated withSnO₂, electric conductive carbon black, powder having high aspect ratiosuch as, for example, potassium titanate whisker coated thereon by Ag orPd, whisker coated thereon by SnO₂, electric conductive carbon whiskers.Particularly, needle type powder may provide an improved volumeresistivity of the electric conductive paste formulation with lowcontents.

The above described electric conductive paste may have volumeresistivity from 10⁻² Ωcm to 10⁶ Ωcm, and it is preferred that theresistance of the electric conductive paste formulation when injected inthe root canal portion may exhibit resistance in an order of theresistance through the periodontal membrane. As described below, if thevolume resistivity is too high, the detection of the paste injection maynot provide sufficiently exact results.

The electric conductive powder maybe present in the electric conductivepaste formulation so as to provide the required volume resistivity tothe electric conductive paste formulation, and the powder may presentfrom 5 wt %˜50 wt % based on the solid of the paste formulation, morepreferably present from 10 wt %˜30 wt % based on the solid of the pasteformulation.

The vehicles may present in the electric conductive paste formulationfrom 10 wt %˜70 wt %, more preferably from 30 wt %˜60 wt %.

Hereinbelow, an exemplary embodiment of the paste formulation includingcalcium hydroxide as its major component and electric conductive metalpowder will be explained.

First, calcium hydroxide is prepared. This calcium hydroxide may be usedunder the specification of Japanese Pharmacopoeia having the particlesize from 10˜50 μm.

In this electric conductive paste, iodoform may preferably be present,because an anti-bacterial activity may be extremely enhanced, and anx-ray imaging performance may be also improved.

In addition, a vehicle described above such as silicone oil etc. may beadded to calcium hydroxide. Addition of the silicone oil may provide ananti-corrosion property to the paste formulation as well as providing anadequate flow performance.

Other additives to the calcium hydroxide may be selected from varioustypes. For example, x-ray contrast agents including bismuth bicarbonate,bismuth sulfate, zirconium silicate may improve the x-ray imagingperformance of the paste.

A dispersion method for the powder may be selected from any well-knownconventional dispersion methods. Especially, when the electricconductive powder having the particle size between 10 and 50 μm is usedas described above, it is possible to apply various mixing and/ordispersion methods, because aggregation of the powder may not be sosevere. In the preparation of the electric conductive paste formulationaccording to the present invention, the paste formulation may beprepared, for example, by providing a paste formulation which ispremixed with calcium hydroxide, iodoform, and silicone oil, adding theelectric conductive powder, mixing the resulting paste formulation againto formulate the electric conductive paste formulation, then filling theresulting electric conductive paste formulation into the injector in aform of a cylinder for use when necessary. However, it is possible tomix a non-conductive powder such as calcium hydroxide and the electricconductive powder together with the vehicle such as silicone oil at thesame time so that as the paste formulation according to the presentinvention may be obtained.

In the above described embodiment, the conductivity/resistivitydescribed above may be obtained by adding electric conductive powdersuch as gold, silver, copper, and nickel having the particle sizedescribed above. Since the electric conductivity is provided with thepaste formulation, and the paste formulation may be injected into theroot canal by an injector implemented with an electric conductivemember, the adequate injection of the paste formulation to the rootcanal may be proved by detecting the resistance. Further, since theelectric conductive powder is added to the paste, and the thermal andelectric conductivities of the paste are improved, good thermal andelectric properties may be obtained. When carbon powder is used, it isexpected to absorb formaldehyde included in form-cresol which is used totreat the root canal and is also included as the major component ofform-cresol.

Referring to figures, an embodiment of the paste injector, which is ableto inject the electric conductive paste formulation into the root canaland simultaneously to measure the electric resistance, will be explainedin detail.

FIG. 1 shows an exploded view of a first embodiment of the pasteinjector 1 according to the present invention. The paste injector 1comprises the container portion 2 for holding the fill electricconducting paste formulation, the insert portion 3 being inserted intothe container portion 2, the injection portion 4 formed as a taperedtube toward the tip and disposed at the front end of the containerportion 2, and the seal member 5 disposed at the end of the insertportion 3 which is inserted to the container portion 2.

The container portion 2 and the insert portion 3 may be made of glass,or synthetic resin such as polypropyrene, polycarbonate, polyvinylchloride. However, when handling performance such as damage isconsidered, the portions 2, 3 may preferably be made of a syntheticresin such as polypropyrene, polycarbonate, polyvinyl chloride. Thecontainer portion 2 has a hollow inside portion within which theelectric conductive paste formulation is held. The container portion 2comprises a projection 2 a at the end opposite to the injection portion4 with which insertion of the insert portion 3 is made easy when fingersare rested thereon. Materials for forming the injection portion 4 may beselected from any suitable materials so that the shape of the taperedtube of the injection portion 4 is formed to be thin and flexible.

The insert portion 3 is used to extrude the electric conductive pasteformulation held in the container portion 2. The seal member 5 disposedat the front end of the insert portion 3 improves the seal between theinner face of the container portion 2 and insert portion 3. Installationof the seal member 5 onto the insert portion 3 may be achieved throughvarious methods including engaging the seal member 5 in the shape ofpipe onto a recess formed to the insert portion 3, or molding the sealmember 5 made of a synthetic resin integrally around the insert portion3.

At the end of the insert portion 3 opposite to the end inserted into thecontainer portion 2 there is included a projection 3 a extending beyondthe diameter of the insert portion 3 so as to make the insert easy byexerting force by fingers when the electric conductive paste formulationis injected into the root canal. The projection 3 a may be formedseparately from the container portion 3 and then may be adhered by sometypes of adhesives as well as being integrally formed with the containerportion 3.

When the electronic conductive paste formulation is injected into theroot canal, the above described paste injector 1 is held by one hand,and holding the projections 2 a, 3 a between the fingers to exert theforce to extrude the electric conductive paste formulation into the rootcanal.

As shown in FIG. 1, the first embodiment of the insert portion 3 of thepaste injector 1 according to the present invention is implemented withthe conductive member. The conductive member comprises the end 6, theterminal 7, the end 8, the terminal 9, and the lead line 10 extendingbetween the end 6 and the end 8. These components form the conductivemember by the end 6 being connected to the terminal 7 formed on the sideof the seal member 5 which contacts the electric conductive pasteformulation. Another end 8 is connected to the terminal 9 extendingoutside the insert portion 3 from the position adjacent projection 3 aformed on the insert portion 3. The lead line 10 extends through theinsert portion 3, thereby the electric conductive paste formulation isconnected electrically outside the insert portion 3. The lead line 10and the terminals 7, 9 may be formed by insert molding when the insertportion 3 is molded, or by inserting them after molding thereof.

FIG. 2 shows an enlarged cross section of the terminal connectingportion of the terminal 9 of the first embodiment of the paste injector1 according to the present invention. FIG. 2(a) shows an enlarged crosssection of the insert portion 3 comprising the terminal 9. As shown inFIG. 2(a), the terminal 9 extends outside the insert portion 3 from aposition adjacent to the projection 3 a and electrode 106 is connectedto the terminal 9 through the clip. FIG. 2(b) shows that the terminal 9is disposed in the projection 3 a, and protrudes outside the insertportion 3 from the lateral side of the projection 3 a. FIG. 2(c) showsthat the terminal 9 has the opening 11 facing outside the insert portion3 into which a needle electrode may be inserted or screwed. FIG. 2(d)shows that the terminal 9 is formed as a band which extendscircumferentially and radially about the insert portion 3 at a positionadjacent to the projection 3 a of the insert portion 3. The arrangementof the terminal 9 illustrated in FIG. 2 may be selected depending oneasiness of handling and operation for the root canal filling, and theconstructions shown in FIG. 2 may be used in any combinations eachother.

FIG. 3 shows a second embodiment of the paste injector 1 according tothe present invention. FIG. 3(a) shows a partial cut away cross sectionof the paste injector 1, and the paste injector 1 comprises thecontainer portion 2 and the insert portion 3 which is inserted into thecontainer portion 2. The injection portion 4 is formed as a tapered tubeand is disposed at the front end of the container portion 2. In FIG.3(a), the container portion 2 is partly cut away to show the electricconductive paste formulation D. In the injection portion 4 of the pasteinjector 1 of the second embodiment according to the present invention,the lead line 10 extends outside the paste injector 1 at about thecurved portion thereof so that the distance between a tip of theinjection portion 4 and the end of the lead line 10 may be substantiallydecreased with respect to the first embodiment so as to reduce adverseeffects of the resistance of the electric conductive paste formulation Don the resistance measurement.

In FIG. 3(b), an enlarged cross section of the curved portion of theinjection portion 4 attached to the paste injector 1 is shown. Thesecond embodiment of the paste injector 1 shown in FIG. 3(b) has thelead line 10 extending through inside path 4 a adjacent to the tip fromthe lead line inlet position formed at the injection portion 4 as closeas possible such that the end 6 may be located adjacent to the tip. fromwhich the electric conductive paste D is injected. When suchconstruction is adopted, the distance between the end 6 and anotherelectrode 104 (not shown) through the electric conductive pasteformulation D may be reduced, thereby reducing the effect on theresistance measurements due to the resistance of the electric conductivepaste formulation D.

When the lead line 10 is drawn out of the paste injector 1 of the secondembodiment according to the present invention, the terminals 9 shown inFIG. 2 may be used. Alternatively, without providing the terminal 9, thelead line 10 is stripped at the both ends to obtain sufficientconductivity such that one end is disposed in the inner path 4 a.Another end may be drawn outside the wall of he injection portion 4 cwhile maintaining seal performance with a heat-seal or the adhesive 4 b.It is of course possible to mold the lead line 10 integrally when theinjection portion 4 is molded. The lead line 10 drawn out of the pasteinjector 1 may be extended to the projection 2 a formed on the containerportion 2 along to the outer lateral side so as not to contact thestripped end to an oral cavity, and thereafter be connected to anelectrode of the apparatus for measuring resistance. The lead line usedmay have any thickness. However, to obtain good handling performancewhile not degrading the injection through the injection portion 4, thelead line 10 may preferably be sufficiently thin. The lead line 10 mayhave a cover, or may not have a cover.

Now, a system for detecting the paste filling will be explainedhereinbelow with referring to FIG. 4-FIG. 7. FIG. 4 shows a conventionalarrangement of a system for measuring the root canal length by theresistance or the impedance. When the root canal length isconventionally measured by the resistance, the operation thereofcomprises steps of; first spreading the root canal portion of thedamaged tooth T, next cleaning the spread root canal 21 by hydrogenperoxide while retaining hydrogen peroxide within the root canal 21, andthen inserting the reamer 20 into the root canal 21.

The resistance measuring device 100 comprises the current detector 101,the power supply 102, the control device 103 including relay circuit,the electrode 104 connected to the damaged tooth through the lip, thecurrent display device 105 including a current indication device and/oran alarm device, and the electrode 106 connected to the end of thereamer 20. The resistance measuring device 100 actuates the currentdisplay device 105 through the control device 103 based on the currentsignal detected by the current detector 101. The resistance measuringdevice 100 acknowledges to the operator that the resistances or thecurrent values become predetermined values, or the top of the reamerreaches to the apical constriction P, or the top of the reamer reachesto the position having a predetermined distance, i.e., about 1 mm fromthe apical constriction P.

Usually, when the reamer 20, reaches the periodontal membrane, theelectric circuit formed between the reamer 20 and the electrode 104,which is connected to a tube contacting a lip and being extended from adental pump, has a resistance about 6.5 kΩ including an internalresistance of the system for resistance measurement. FIG. 5 shows aschematic illustration of the resistances. In FIG. 5, the resistance ofthe reamer 20 is shown by the reference numeral R1. As shown in FIG. 5,the reamer 20, the periodontal membrane, and the electrode 104 usuallyconnected to the dental tube form an electric circuit including aresistance R1. Usually, the inside of the root canal in which the reamer20 is inserted is cleaned and is almost dried under the measurement.Therefore, the current may not substantially flow in the circuit.However, the current begins to flow due to effects of exudate, and/orconductivity of hydrogen peroxide used in the cleaning process andremained therein as the top of the reamer 20 moves toward theperiodontal membrane. When the reamer 20 reaches the periodontalmembrane, the entire circuit resistance becomes the above explainedresistance of about 6.5 kΩ.

The present invention uses the electric conductive paste formulation Das a probe electrode rather than using the reamer 20 as the probeelectrode for the measurement of the root canal length.

FIG. 6 shows an arrangement when the electric conductive pasteformulation is filled in the root canal 21 of the damaged tooth T usingthe paste injector 1 according to the first embodiment of the presentinvention. As shown in FIG. 6, the terminal 9 is connected to theelectrode 106 of the resistance measurement device 100, and theelectrode 104 of the resistance measurement device 100 is connected tothe dental tube. In the condition illustrated in FIG. 6, no current, orvery low current flows through the current detecting device 101, andthen the resistance is held high.

FIG. 7 shows the filling process of the electric conductive pasteformulation D into root canal 21 using the same arrangement shown inFIG. 6 while the paste injector 1 according to the second embodiment ofthe present invention is used. As shown in FIG. 7, as the filling of theelectric conductive paste formulation D proceeds and the electricconductive paste formulation D becomes closer to the apical constrictionP, a week current starts to flow through the electric conductive pasteformulation D. Finally the electric conductive paste D contacts theperiodontal membrane, and then the resistance R1 of the reamer 20 isreplaced to the resistance R2. The resistance R2 depends on the distancebetween the position where the lead line 10 contacts the electricconductive paste formulation D within the injection portion 4 and theperiodontal membrane. Therefore, the detection of the filing of theelectric conductive paste formulation D to the apical constriction P isdetermined by monitoring the resistance to be (6.5 kΩ−R1+R2).Alternatively, the relation between the distance from the periodontalmembrane to the electric conductive paste formulation D includingconductive metals, or conductive metal oxides and the resistance ispreviously measured by x-ray photographs, and then the distance from theperiodontal membrane may be estimated when the resistance reaches acertain resistance higher than (6.5 kΩ−R1+R2). As described above, sincethe present invention uses the paste formulation filled in the rootcanal as the current probe, once the resistance reaches the abovecertain value, it is determined that the filling of the root canal bythe paste formulation is completed. The construction described aboveallows the reduction of the complexity of root canal filing and/orinjection operation that previously requires duplex steps; measuring theroot canal length by the impedance, and next spreading the root canalportion and then inserting the gutta percha point to complete thefilling of the root canal. In addition, the detection of whether or notthe paste formulation is sufficiently filled within the root canalbecomes easy, whereas such detection is regarded to be difficult in theconventional root canal filling/injection operation. Therefore, thepresent invention can provide a system for detecting paste filling whichmakes the measurement more speedy and easier, and that insures thefilling of the paste formulation.

The power supply 102 used may be selected from a direct current type oran alternating current type, and the value of R2 and the internalresistance etc. may be selected as requested. The measurement etc. maybe achieved through resistance measurement or impedance measurementdepending on the kinds of the power supplies used. It may possible toalarm the operator to pay attention when the predetermined workinglength is obtained.

Hereafter, the present invention will be explained in detail byexamples, however, these examples are provided only for explanation ofthe present invention and do not intend to limit the scope of thepresent invention.

EXAMPLES Example 1

To a solid component including 50 wt % of calcium hydroxyde, iodoform 20wt %, 30 wt % of silicone oil was added and mixed to prepare a pasteformulation.

To this paste formulation, further 10 wt % of a silver powder based onthe weight of the above solid component was added and mixed to form apaste formulation according to the present invention. The current of 5mA was flowed in the resultant electric conductive paste formulation asmeasured by an ampere meter. Next, a lead line having 0.1 mm diameterwas inserted into an injection portion of a commercially available pasteinjector so as to prepare the paste injector according to the presentinvention as shown in FIG. 3. The electric conductive paste as preparedabove was filled in the paste injector, and the paste discharge throughthe tip portion was confirmed.

A circuit illustrated in FIG. 8 was constructed using a pulpless toothand injecting the electronic conductive paste formulation into the rootcanal 21 using the paste injector in order to operate the root canalfilling. The front end of the electrode 104 of the resistancemeasurement device 100 was located inside the root canal 21 slightlyabove the apical constriction P. As the injections of the electricconductive paste formulation was started and proceeded, the currentdetector 101 detected the current through the circuit shown in FIG. 8.

Thereafter, the injection portion of the paste injector was pulled outcarefully from the pulpless tooth, and an x-ray photograph was taken toobserve the filling condition of the electric conductive pasteformulation. It was confirmed that the electric conductive pasteformulation reached to the apical constriction P. That is, the detectionof the circuit formation by the electric conductive paste formulationreached to the apical constriction P indicated the completion of theroot canal filling.

Example 2

40 wt % of hydroxy apatite, 10 wt % of barium sulfate, 50 wt % ofsilicone oil were mixed together to form the paste formulation. Aupowder of 25 wt % was mixed to the above paste formulation. The currentof 3 mA flowed in the resultant paste as measured by the ampere meter.The resultant electric conductive paste formulation was used in the sametest as described in the Example 1. It was confirmed that the electricconductive paste was filled in the apical constriction P of the damagedtooth.

INDUSTRIAL AVAILABILITY

As described above, since the present invention uses the pasteformulation filled in the root canal as the current probe, thecompletion of the paste formulation into the root canal is immediatelydetected when the resistance becomes the above described value.Therefore, conventional duplex procedures comprising measuring the rootcanal length by the impedance measurement, next spreading the rootcanal, and then inserting the gutta percha point so as to fill the rootcanal is not required. In addition, the detection whether or not thepaste is entirely filled in the root canal becomes easy, which wasdifficult in the conventional root canal filling operation using paste.The present invention may provide the system for detecting of pastefilling which is carried out more speedy and easier while insuring thesufficient filling of the paste.

The present invention has been explained by non-limiting exemplaryexamples, however, it is appreciated by a person skilled in the art thatmany other variations, modifications, and omissions may be possiblewithin the scope of the invention as described in the appended claims.True scope of the present invention will only be limited by the claims.

What is claimed is:
 1. A paste formulation for dental use: comprising amixed formulation having 5-50 weight % of metal powder based on a solidcomponent of said paste formulation; at least one compound selected fromthe group consisted of calcium hydroxide, hydroxy apatite and tricalciumphosphate; and at least one vehicle selected from the group consisted ofsilicone oil, guaiacol formaldehyde mixture, propylene glycol, dryethanol, caster oil, liquid paraffin wherein said paste formulationincludes the powder selected from the group consisting of: inorganicpowder coated with metal; carbon powder; carbon whiskers; and potassiumtitanate whiskers coated with metal.
 2. The paste formulation for dentaluse according to claim 1, wherein said paste formulation includes atleast one X-ray contrast agent selected from the group consisting ofiodoform, barium sulfates anhydrous zinc sulfate, aluminum sulfate, andzinc oxide.
 3. The paste formulation for dental use according to claim1, wherein said at least one compound selected from the group consistingof calcium hydroxide, hydroxy apatite and tricalcium phosphate, ispresent in not less than 30 wt % based on said solid of said pasteformulation.
 4. The paste formulation for dental use according to claim1, wherein the formulation is premixed.